Si-controlled dimmer and electro-transistor dimmer (for short dimmer) can adjust brightness of tungsten lamp. Referring to FIG. 1, on-time of dimmer 5 is determined by charging time of capacitance 9 of circuit, and therefore change conduction angle of sinusoidal alternating current non-sinusoidal waveforms, and thus change current of the tungsten lamp 10 so as to adjust brightness, which is defined as leading edge technology. As indicated in FIG. 1, dimmer 5 is connected with tungsten lamp 10 in series. Current passes through fuse 1, inductance 2, Potentiometer 7, resistance 8, capacitance 9, and tungsten lamp 10 to form a charging loop of charging capacitance 9. The charging time of the capacitance 9 is determined by resistance of the potentiometer 7. When charging of the capacitance 9 is finished after a predetermined time, the capacitance 9 triggers control end of the dimmer 5 via trigger diode 6 to make dimmer 5 conductive. Because the tungsten lamp 10 is resistance load, a voltage waveform 1 is consistent with current waveform 3 (referring to FIG. 2) after edge of dimmer, and the on-time is same as off-time. Therefore, the adjusting of brightness of the tungsten lamp 10 is achieved.
LED is energy-saving and new lamp. The power of LED is much smaller than tungsten lamp. LED is a low-voltage direct current element. LED lamp need to be equipped with a LED driving power supply so as to be drived to illuminate. LED driving-switch power supply is capacitive load and is not equipped with dimmer control circuit. When the tungsten lamp 10 is replaced by LED lamp with switch power supply, the on-time of the dimmer 5 is shorter than that of voltage (referring to FIG. 3). When there is no current passing through the dimmer 5, there is voltage existed between the resistance 7 and the capacitance 9. This voltage charges for the capacitance 9. When charging for a predetermined time, the dimmer 5 is triggered, the dimmer 5 is in on-time twice in a half-period. LED lamp flashes frequently because of intermittence of input of driving-switch power supply. Therefore, the dimmer cannot adjust brightness of LED lamp with Internal/External Auto-switch
Therefore, a dimmer device adapted for use in dimmer is desired to overcome the above-described shortcomings.